Prior processes for extrusion of recycled plastic for purposes of molding certain articles have been limited by the fact that the feed stock must be subjected to significant and costly pre-process steps. Also, the commercial viability of these processes has been limited by the size and physical properties of the resulting article. For example, in the production of plastic lumber, the profiles are limited to thicknesses of greater than one inch, the lengths are restricted to standard mold sizes and a maximum of 14 feet, the tensile strength and stiffness are sufficient for only light loads and short spans, residual moisture cannot be devolatized without drying equipment, post-melt additives cannot be introduced, mechanical reinforcement agents such as continuous inorganic fiber rovings cannot be introduced, and the production volume is low thus substantially increasing unit cost. Systems that use recycled plastic typically will not accommodate commingled, contaminated feed stock and often require resins to be segregated and the feed stock to be washed. Moreover, because these systems do not allow for mechanical reinforcement, the lumber they produce has insufficient tensile strength for use in critical load-bearing applications.
In a number of industrial applications, such as the production of pallets for use in warehouses, the nominal dimension of the decking boards or slats are typically 1".times.4" or 1".times.6". Other applications also require a thin profile board so as to limit the weight and size of the overall product as well as the amount of material being used. In commingled, contaminated feed stock, such thin profiles have not been possible due to the mixture of dissimilar resins introduced with the feed stock. Each resin has a different melting temperature, melt index, and melt strength, among other characteristics, which creates limitations in the final extrusion of the product. Moreover, in order to maintain sufficient stiffness of the final product, it has often been required to increase the thickness of the product as well as limit its overall length or span.